A Protein Phosphatase from Human T Cells Augments Tat Transactivation of the Human Immunodeficiency Virus Type 1 Long-Terminal Repeat

Bharucha, Diana C.; Zhou, Meisheng; Nekhai, Sergeï; Brady, John; Shukla, Ram R.; Kumar, Ajit

doi:10.1006/viro.2002.1438

Cited by 22 publications

(25 citation statements)

References 43 publications

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“…Thus, PP2A might positively regulate HIV-1 transcription. Our studies showed that PP1 is also a positive regulator of HIV-1 transcription in vitro (18,19) and in vivo (20). Indeed, in a previous study we showed that inhibition of nuclear PP1 potently inhibited Tat-induced transcription (20).…”

supporting

confidence: 59%

“…In a previous study we found that GST-Tat binds a phosphatase from partially purified cellular extract and that this phosphatase was inhibited at a low concentration of okadaic acid, indicating that it was PP1 (18). In the present study we delineated two distinct regions of Tat that might interact with PP1 by using enzymatic kinetics and competition assays.…”

Section: Discussionmentioning

confidence: 65%

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Nuclear Targeting of Protein Phosphatase-1 by HIV-1 Tat Protein

Ammosova

Jerebtsova

Beullens

et al. 2005

Journal of Biological Chemistry

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Transcription of human immunodeficiency virus (HIV)-1 genesis activated by HIV-1 Tat protein, which induces phosphorylation of the C-terminal domain of RNA polymerase-II by CDK9/cyclin T1. We previously showed that Tat-induced HIV-1 transcription is regulated by protein phosphatase-1 (PP1). In the present study we demonstrate that Tat interacts with PP1 and that disruption of this interaction prevents induction of HIV-1 transcription. We show that PP1 interacts with Tat in part through the binding of Val 36 and Phe 38 of Tat to PP1 and that Tat is involved in the nuclear and subnuclear targeting of PP1. The PP1 binding mutant Tat-V36A/ F38A displayed a decreased affinity for PP1 and was a poor activator of HIV-1 transcription. Surprisingly, Tat-Q35R mutant that had a higher affinity for PP1 was also a poor activator of HIV-1 transcription, because strong PP1 binding competed out binding of Tat to CDK9/cyclin T1. Our results suggest that Tat might function as a nuclear regulator of PP1 and that interaction of Tat with PP1 is critical for activation of HIV-1 transcription by Tat. Human immunodeficiency virus type 1 (HIV-1)3 is a retrovirus that encodes transcriptional activator (Tat) protein. The activation domain of Tat (amino acids 1-48) interacts with host cell factors, whereas the positively charged RNA-binding domain (amino acids 49 -57) interacts with HIV-1 transactivation response (TAR) RNA (1). In cell-free transcription assays Tat induces elongation of transcription (2, 3). In vivo, Tat also induces initiation of transcription from the integrated HIV-1 promoter (4 -6). In a recent study Tat was shown to stimulate formation of a transcription complex containing TATA box-binding protein but not TATA box-binding protein-associated factors, thus indicating that Tat may enhance initiation of transcription (4). This finding apparently agrees with the early observation that Tat binds directly to the TATA box-binding protein-containing basal transcription factor TFIID (7). Tat activates HIV-1 transcription by recruiting transcriptional coactivators that include positive transcription elongation factor b, containing CDK9/cyclin T1, an RNA polymerase II CTD kinase (3,8,9) and histone acetyltransferases (10 -12). Whereas positive transcription elongation factor b induces HIV-1 transcription from non-integrated HIV-1 template (3,8,9), histone acetyltransferases allow induction of integrated HIV-1 provirus (10 -12). In contrast to the well defined role of protein kinases, the role of protein phosphatases in Tat-mediated HIV-1 transcription is less well understood. FCP1, a CTD phosphatase that dephosphorylates Ser-2 during elongation of transcription (13), is inhibited by Tat and this inhibition may alleviate FCP1-mediated pausing of transcription (14,15). In addition to FCP1, PP2A and PP1 were also shown to be involved in the regulation of HIV-1 transcription. Disregulation of cellular enzymatic activity of PP2A inhibited Tat-induced HIV-1 transcription (16). Expression of the catalytic subunit of PP2A enhanced activa...

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confidence: 59%

Section: Discussionmentioning

confidence: 65%

Nuclear Targeting of Protein Phosphatase-1 by HIV-1 Tat Protein

Ammosova

Jerebtsova

Beullens

et al. 2005

Journal of Biological Chemistry

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“…Moreover, PP1 was shown to act as a major CTD phosphatase in nuclear extracts and to affinity-purify with RNA polymerase II. Both PP1 and the nuclear regulator NIPP1 have also been identified as components of the Tat-associated RNA polymerase II complex, which regulates transcription from the human immunodeficiency virus type 1 promoter (40,275).…”

Section: A Transcriptionmentioning

confidence: 99%

Functional Diversity of Protein Phosphatase-1, a Cellular Economizer and Reset Button

Ceulemans

Bollen

2004

Physiological Reviews

605

584

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Ceulemans, Hugo, and Mathieu Bollen. Functional Diversity of Protein Phosphatase-1, a Cellular Economizer and Reset Button. Physiol Rev 84: 1–39, 2004; 10.1152/physrev.00013.2003.—The protein serine/threonine phosphatase protein phosphatase-1 (PP1) is a ubiquitous eukaryotic enzyme that regulates a variety of cellular processes through the dephosphorylation of dozens of substrates. This multifunctionality of PP1 relies on its association with a host of function-specific targetting and substrate-specifying proteins. In this review we discuss how PP1 affects the biochemistry and physiology of eukaryotic cells. The picture of PP1 that emerges from this analysis is that of a “green” enzyme that promotes the rational use of energy, the recycling of protein factors, and a reversal of the cell to a basal and/or energy-conserving state. Thus PP1 promotes a shift to the more energy-efficient fuels when nutrients are abundant and stimulates the storage of energy in the form of glycogen. PP1 also enables the relaxation of actomyosin fibers, the return to basal patterns of protein synthesis, and the recycling of transcription and splicing factors. In addition, PP1 plays a key role in the recovery from stress but promotes apoptosis when cells are damaged beyond repair. Furthermore, PP1 downregulates ion pumps and transporters in various tissues and ion channels that are involved in the excitation of neurons. Finally, PP1 promotes the exit from mitosis and maintains cells in the G1or G2phases of the cell cycle.

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“…The HIV-1 Tat prevents the formation of the large complex and promotes the dissociation of CDK9/cyclin T1 from 7SK RNA/HEXIM1 complex (15). (20) and in cultured cells (21). PP1 holoenzymes consist of a constant catalytic subunit (PP1␣, PP1␤/␦, or PP1␥) and a variable regulatory subunit that determines the localization, activity, and substrate specificity of the phosphatase (22, 23).…”

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confidence: 99%

“…In normally growing cells, protein phosphatase M1A (PPM1A) dephosphorylates CDK9 on Thr 186 (19). Our previous studies showed that PP1 stimulates Tat-dependent HIV-1 transcription in vitro (20) and in cultured cells (21). PP1 holoenzymes consist of a constant catalytic subunit (PP1␣, PP1␤/␦, or PP1␥) and a variable regulatory subunit that determines the localization, activity, and substrate specificity of the phosphatase (22,23).…”

mentioning

confidence: 99%

Expression of a Protein Phosphatase 1 Inhibitor, cdNIPP1, Increases CDK9 Threonine 186 Phosphorylation and Inhibits HIV-1 Transcription

Ammosova

Yedavalli

Niu

et al. 2011

Journal of Biological Chemistry

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Cyclin-dependent kinase-9 (CDK9) 3 /cyclin T1 is a protein kinase that phosphorylates the C-terminal domain of the largest subunit of RNA polymerase II during transcription elongation (1). CDK9/cyclin T1 is part of positive transcription elongation complex (P-TEFb) and present in the cells within large and small complexes. The large complex contains 7SK RNA (2, 3) and the hexamethylene bisacetamide-induced protein (HEXIM1) (4, 5). The activity of CDK9 in the large complex is inhibited by the interaction with 7SK RNA and HEXIM1 (2-5). In stress-induced cells, CDK9/cyclin T1 dissociates from the 7SK RNA and HEXIM1 protein and then binds to the bromodomain protein 4 (Brd4) (6, 7), a member of bromodomain-containing extraterminal domain protein family that interact with acetylated histones. CDK9/cyclin T1 bound to Brd4 forms the transcriptionally active P-TEFb (7). Brd4 recruits P-TEFb to the promoters of cellular genes that are expressed at the end of mitosis (8). HIV-1 Tat protein can also recruit P-TEFb by binding directly to CDK9/cyclin T1 and targeting it to HIV-1 TAR RNA (7). Hence, Tat induces HIV-1 transcription by recruiting CDK9/cyclin T1 (9 -11) and histone acetyltransferases to the HIV-1 promoter (7,(12)(13)(14). The HIV-1 Tat prevents the formation of the large complex and promotes the dissociation of CDK9/cyclin T1 from 7SK RNA/HEXIM1 complex (15). (20) and in cultured cells (21). PP1 holoenzymes consist of a constant catalytic subunit (PP1␣, PP1␤/␦, or PP1␥) and a variable regulatory subunit that determines the localization, activity, and substrate specificity of the phosphatase (22, 23). One of the major nuclear regulators of PP1 is NIPP1 (nuclear inhibitor of PP1), which inhibits the dephosphorylation of a wide range of PP1 substrates (22, 23). Tat-mediated HIV-1 transcription is blocked by the expression of NIPP1, and the inhibition is reversed by the co-expression of PP1␥ (21). Tat contains a PP1-binding The abbreviations used are: CDK9, cyclin-dependent kinase-9; Brd4, bromodomain protein 4; cdNIPP1, central domain NIPP1; EGFP, enhanced green fluorescent protein; HEXIM1, hexamethylene bisacetamide-induced protein; NIPP1, nuclear inhibitor of PP1; P-TEFb, positive transcription elongation complex; PP1, protein phosphatase 1; PP1C, catalytic subunit of PP1; PP2B, protein phosphatase 2B; PPM1A, protein phosphatase M1A; TAR RNA, transactivation response RNA.

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A Protein Phosphatase from Human T Cells Augments Tat Transactivation of the Human Immunodeficiency Virus Type 1 Long-Terminal Repeat

Cited by 22 publications

References 43 publications

Nuclear Targeting of Protein Phosphatase-1 by HIV-1 Tat Protein

Nuclear Targeting of Protein Phosphatase-1 by HIV-1 Tat Protein

Functional Diversity of Protein Phosphatase-1, a Cellular Economizer and Reset Button

Expression of a Protein Phosphatase 1 Inhibitor, cdNIPP1, Increases CDK9 Threonine 186 Phosphorylation and Inhibits HIV-1 Transcription

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